In North America, drinking water is chlorinated prior to discharge to distribution for public consumption in order to prevent biological contaminants from forming in the distribution prior to consumer use/consumption. In practice, such chlorination would occur after the water has undergone any biological decontamination processes in order to prevent the formation of biological contaminants after such processing. However, typically no biological treatment processes are even used for drinking water systems, and are instead limited to use in sanitary water applications.
While successful in preventing biological contaminants from forming in the distribution, one of the major drawbacks from this chlorination practice is that the chlorine will react with naturally occurring matter (NOM) present in the water. This reaction can form toxic chemicals called trihalomethanes (THMs) and haloacetic acids (HAAs). Although such toxic chemicals are dangerous to consumers, current laws are somewhat loose in regulating the allowable concentration of THMs and HAAs in drinking water. In face of ever-increasing environmental concerns, more stringent regulations are being implemented to greatly reduce the amounts of allowable THMs and HAAs in drinking water, in some cases down to about 80 parts per billion along the entire lengths of the distribution lines.
In order to combat the formation of THMs and HAAs, some water treatment plants have included the addition of ammonia, in addition to the chlorine, to produce chloramines in the water. Chloramines are less aggressive at creating THMs and HAAs when reacting with NOM, however, they are also less aggressive at disinfection as well when compared to free chlorine.
Other common water treatment practices include coagulation, sedimentation, filtration and disinfection. In such approaches, organic matter is coagulated and allowed to settle, with the water then filtered and disinfected. Although such a coagulation-based approach is effective at removing high molecular weight organics, such as lignins and tannins, from the water, such an approach does not provide effective pretreatment to the THM and HAA precursors, as the precursors tend to be small molecular weight compounds. Still other approaches involve alternative oxidation processes (AOPs) where an oxidant, such as ozone or hydrogen peroxide or other aggressive oxidant, is added to the water. While somewhat successful in eliminating THM and HAA precursors, such AOPs require an additional step to remove the residual oxidant added to the water. Accordingly, what is needed is a system and process for eliminating the formation of THMs and HAAs in the drinking water distributed for public consumption that does not suffer from the deficiencies of the conventional approaches. This disclosure addresses the deficiencies of conventional approaches.